1. Field of the Invention:
This invention relates to an evacuated blood collecting device and more particularly to an evacuated blood collecting device capable of protracted retention of a vacuum therein.
2. Description of Prior Art:
The method for collection of blood under a vacuum has found widespread acceptance because it entails hemolysis or coagulation only to a minimal extent and secures a blood sample hardly suffering from contamination or evaporation and, in terms of efficiency of work involved, simplifies preparations for blood collection and management of utensils. The evacuated blood-collecting device which is adopted for this method comprises a cylindrical receptacle and a puncturable rubber stopper for tightly sealing the cylindrical receptacle. The interior of the tightly sealed cylindrical receptacle is kept under a vacuum. This device effects desired collection of blood by having one end of a blood collection needle pierced into the blood vessel of a subject and the other end of the needle pierced through the rubber stopper into the receptacle thereby establishing communication between the blood vessel and the interior of the receptacle and enabling the blood to flow into the receptacle owing to the negative pressure in the receptacle. In the evacuated blood-collecting device of this type which has heretofore found utility in clinical applications, the cylindrical receptacle has been made of glass to meet the conditions of imperviousness to gas and high transparency and the stopper has been made of butyl rubber to meet the conditions of minimal perviousness to gas and high puncturability.
Unfortunately, the cylindrical receptacle made of glass has the disadvantage that it is liable to breakage during storage, transportation or actual use and it is heavy. Studies have been made, therefore in search for a cylindrical receptacle made of a synthetic resin featuring light weight and transparency, only to demonstrate that since every synthetic resin is more or less pervious to gas, the cylindrical receptacle made of any synthetic resin while in protracted storage permits the ambient gas such as, for example, air to pass into the tightly sealed evacuated blood collecting device and, as the result, the pressure within the syringe gradually rises possibly to the extent of making ineffectual the required blood collection under a vacuum. An attempt to adopt an evacuated blood collecting device made of a synthetic resin has inevitably necessitated use of a vacuum package to ensure safe preservation. The preservation by the use of a vacuum package, however, has the disadvantage of high cost because the package which by nature is required to keep its interior under a vacuum is very expensive and entails much time and labor when it is closed to seal its content when it is subsequently opened preparatory to putting the content to use.
Moreover, since the butyl rubber polymer which forms the basic material for the stopper of butyl rubber does not possess, in itself, properties necessitated by this particular product, it is inevitably required to undergo complicated steps such as the incorporation of adjuvants including sulfur and a vulcanization promotor. Further, the fabrication of the stopper using this polymer has the disadvantage of heavy loss of material because it gives rise to lots of burrs which cannot be reclaimed. Through incorporation of a thermoplastic elastomer, this polymer may be converted into a material capable of being reclaimed after molding. The stopper made of this modified polymer, however, has the disadvantage that it is more pervious to gas than the stopper made of butyl rubber.